When Defense Secretary Robert Gates devoted his final policy speech this month to berating NATO and our European allies, he was engaging in a time-honored tradition: Americans have worried about Europeans shirking their share of global burdens since the start of the 60-year-old alliance.

Gates sounded a pessimistic note, warning of “the real possibility for a dim if not dismal future for the transatlantic alliance.” Yet, the outgoing Pentagon chief may not have been pessimistic enough. The U.S.-European partnership that proved so central to managing and winning the Cold War will inevitably play a far diminished role in the years to come. To some extent, we’re already there: If NATO didn’t exist today, would anyone feel compelled to create it? The honest, if awkward, answer is no.

In the coming decades, Europe’s influence on affairs beyond its borders will be sharply limited, and it is in other regions, not Europe, that the 21st century will be most clearly forged and defined.

Certainly, one reason for NATO’s increasing marginalization stems from the behavior of its European members. The problem is not the number of European troops (there are 2 million) nor what Europeans collectively spend on defense ($300 billion a year), but rather how those troops are organized and how that money is spent. With NATO, the whole is far less than the sum of its parts. Critical decisions are still made nationally; much of the talk about a common defense policy remains just that — talk. There is little specialization or coordination. Missing as well are many of the logistical and intelligence assets needed to project military force on distant battlefields. The alliance’s effort in Libya — the poorly conceived intervention, the widespread refusal or inability to participate in actual strike missions, the obvious difficulties in sustaining intense operations — is a daily reminder of what the world’s most powerful military organization cannot accomplish.

With the Cold War and the Soviet threat a distant memory, there is little political willingness, on a country-by-country basis, to provide adequate public funds to the military. (Britain and France, which each spend more than 2 percent of their gross domestic products on defense, are two of the exceptions here.) Even where a willingness to intervene with military force exists, such as in Afghanistan, where upward of 35,000 European troops are deployed, there are severe constraints. Some governments, such as Germany, have historically limited their participation in combat operations, while the cultural acceptance of casualties is fading in many European nations.

But it would be wrong, not to mention fruitless, to blame the Europeans and their choices alone. There are larger historical forces contributing to the continent’s increasing irrelevance to world affairs.

Ironically, Europe’s own notable successes are an important reason that transatlantic ties will matter less in the future. The current euro zone financial crisis should not obscure the historic accomplishment that was the building of an integrated Europe over the past half-century. The continent is largely whole and free and stable. Europe, the principal arena of much 20th-century geopolitical competition, will be spared such a role in the new century — and this is a good thing.

The contrast with Asia could hardly be more dramatic. Asia is increasingly the center of gravity of the world economy; the historic question is whether this dynamism can be managed peacefully. The major powers of Europe — Germany, France and Great Britain — have reconciled, and the regional arrangements there are broad and deep. In Asia, however, China, Japan, India, Vietnam, the two Koreas, Indonesia and others eye one another warily. Regional pacts and arrangements, especially in the political and security realms, are thin. Political and economic competition is unavoidable; military conflict cannot be ruled out. Europeans will play a modest role, at best, in influencing these developments.

If Asia, with its dynamism and power struggles, in some ways resembles the Europe of 100 years ago, the Middle East is more reminiscent of the Europe of several centuries before: a patchwork of top-heavy monarchies, internal turbulence, unresolved conflicts, and nationalities that cross and contest boundaries. Europe’s ability to influence the course of this region, too, will be sharply limited.

Political and demographic changes within Europe, as well as the United States, also ensure that the transatlantic alliance will lose prominence. In Europe, the E.U. project still consumes the attention of many, but for others, especially those in southern Europe facing unsustainable fiscal shortfalls, domestic economic turmoil takes precedence. No doubt, Europe’s security challenges are geographically, politically and psychologically less immediate to the population than its economic ones. Mounting financial problems and the imperative to cut deficits are sure to limit what Europeans can do militarily beyond their continent.

Moreover, intimate ties across the Atlantic were forged at a time when American political and economic power was largely in the hands of Northeastern elites, many of whom traced their ancestry to Europe and who were most interested in developments there. Today’s United States — featuring the rise of the South and the West, along with an increasing percentage of Americans who trace their roots to Africa, Latin America or Asia — could hardly be more different. American and European preferences will increasingly diverge as a result.

Finally, the very nature of international relations has also undergone a transformation. Alliances, whether NATO during the Cold War or the U.S.-South Korean partnership now, do best in settings that are highly inflexible and predictable, where foes and friends are easily identified, potential battlefields are obvious, and contingencies can be anticipated.

Almost none of this is true in our current historical moment. Threats are many and diffuse. Relationships seem situational, increasingly dependent on evolving and unpredictable circumstances. Countries can be friends, foes or both, depending on the day of the week — just look at the United States and Pakistan. Alliances tend to require shared assessments and explicit obligations; they are much more difficult to operate when worldviews diverge and commitments are discretionary. But as the conflicts in Iraq, Afghanistan and now Libya all demonstrate, this is precisely the world we inhabit.

For the United States, the conclusions are simple. First, no amount of harping on what European governments are failing to do will push them toward what some in Washington want them to do. They have changed. We have changed. The world has changed.

Second, NATO as a whole will count for much less. Instead, the United States will need to maintain or build bilateral relations with those few countries in Europe willing and able to act in the world, including with military force.

Third, other allies are likely to become more relevant partners in the regions that present the greatest potential challenges. In Asia, this might mean Australia, India, South Korea, Japan and Vietnam, especially if U.S.-China relations were to deteriorate; in the greater Middle East, it could again be India in addition to Turkey, Israel, Saudi Arabia and others.

None of this justifies a call for NATO’s abolition. The alliance still includes members whose forces help police parts of Europe and who could contribute to stability in the Middle East. But it is no less true that the era in which Europe and transatlantic relations dominated U.S. foreign policy is over. The answer for Americans is not to browbeat Europeans for this, but to accept it and adjust to it.

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